Image forming apparatus and low power driving method thereof

ABSTRACT

An image forming apparatus having a USB communication function includes a control interface unit to perform USB control communication, a data interface unit to perform USB data communication, and a control unit to perform an event in a low power mode according to a signal input through the control interface unit, and to perform an event in a normal mode according to a signal input through the control interface unit and the data interface unit. Therefore, the low power mode may be effectively implemented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromKorean Application No. 2009-0084921, filed Sep. 9, 2009, in the KoreanIntellectual Property Office, the disclosure of which is incorporatedherein by reference.

BACKGROUND

1. Field

Aspects relate to an image forming apparatus and a low power drivingmethod thereof.

2. Description of the Related Art

A low power mode is a mode in which the power supply to most of themodules is shut down or minimized so as to minimize power consumptionwhen a system is inactive. In order to implement lower standby power,the power supply may be shut down to main memory (in general, externaldynamic random access memory (DRAM)), or the main memory may enter selfrefresh state and internal memory (in general, internal static randomaccess memory (SRAM)) which is not in use in system on chip (SOC) drivesa program. SRAM usually uses small quantity of memory of approximately128 kilobytes.

However, as in a Universal Serial Bus (USB) driver for printers orlarge-capacity storage devices, if bulk data transmission is required orthe number of supportable interfaces is increased, space taken up by astack is increased, so it is difficult to implement all functions of theUSB driver in a small-capacity SRAM.

In addition, it is inefficient to apply large-capacity SRAM of a highcost.

If a device which is used as a USB device cuts off the power supply tothe external DRAM so as to enter the low power mode, a USB driver in theexternal DRAM also stops its operation, so the device cannot communicatewith a USB and a host device. In particular, if the host device, forexample, a personal computer (PC) sends a specific operation command,for example, a printing command to the device through the USB, the hostdevice cannot perform the command (that is, the PC recognizes thatconnection with the device is cut.). Accordingly, in a related art, theexternal DRAM should operate normally in the low power mode.

If power is continuously supplied to the external DRAM, standby power isconsumed. To consume lower power, if the power supply is cut off to theexternal DRAM, the USB driver does not operate, so communication throughthe USB may be impossible. In this case, if a program which monitors thestate of the device using the USB approaches, it is determined that thedevice is turned off, thereby causing inconvenience. For example, if thePC is connected to the printer through the USB and has a printermonitoring program, when the DRAM of the printer is turned off and theUSB driver does not operate, the PC may recognize that the printer is inan abnormal state or connection with the printer is cut off.

Therefore, there is a need for a low power driving method of an imageforming apparatus.

SUMMARY

Aspects provide an image forming apparatus and a low power drivingmethod thereof.

Additional aspects and/or advantages will be set forth in part in thedescription which follows and, in part, will be apparent from thedescription, or may be learned by practice of the invention.

In accordance with an exemplary embodiment, there is provided an imageforming apparatus including a control interface unit to performUniversal Serial Bus (USB) control communication, a data interface unitto perform USB data communication, and a control unit to perform anevent in a low power mode according to a signal input through thecontrol interface unit, and to perform an event in a normal modeaccording to a signal input through the control interface unit and thedata interface unit.

According to an aspect, in the low power mode, if a signal is inputthrough the data interface unit, the control unit may convert the lowpower mode into the normal mode.

According to an aspect, the image forming apparatus may further includea first memory unit to be used in the normal mode, a second memory unitto be used in the low power mode, and a power supply unit to supplypower to the first memory unit and the second memory unit, wherein ifthe image forming apparatus operates in the low power mode, the controlunit controls the power supply unit to cut off the power supply to thefirst memory unit.

According to an aspect, the control unit may include a main controllerto control operation of the image forming apparatus in the normal mode,and a sub-controller to control operation of the image forming apparatusin the low power mode.

According to an aspect, in the low power mode, the sub-controller maycheck whether or not interrupt is caused by the control interface unitor the data interface unit.

According to an aspect, if interrupt is caused by the control interfaceunit, the sub-controller may process an event related to the interrupt,and if interrupt is caused by the data interface unit, thesub-controller may convert the low power mode into the normal mode.

According to an aspect, the control interface unit may be a control endpoint, and the data interface unit may be a bulk type IN/OUT end point.

In accordance with another exemplary embodiment, there is provided a lowpower driving method of an image forming apparatus which includes acontrol interface unit to perform Universal Serial Bus (USB) controlcommunication, and a data interface unit to perform USB datacommunication, the method including checking whether or not a signal isinput though the control interface unit or the data interface unit in alow power mode, and if a signal is input through the control interfaceunit, performing an event according to the input signal, and if a signalis input through the data interface unit, converting the low power modeinto a normal mode.

According to an aspect, the method may further include if the imageforming apparatus operates in the low power mode, cutting off the powersupply to a first memory unit which is used in the normal mode, andmaintaining the power supply to a second memory unit which is used inthe low power mode.

According to an aspect, the method may further include if the imageforming apparatus operates in the low power mode, cutting off the powersupply to a main controller which controls operation of the imageforming apparatus in the normal mode, and maintaining the power supplyto a sub-controller which controls operation of the image formingapparatus in the low power mode.

According to an aspect, the control interface unit may be a control endpoint, and the data interface unit may be a bulk type IN/OUT end point.

In addition to the exemplary embodiments and aspects as described above,further aspects and embodiments will be apparent by reference to thedrawings and by study of the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the present disclosure will become apparentfrom the following detailed description of exemplary embodiments and theclaims when read in connection with the accompanying drawings, allforming apart of the disclosure of this invention. While the followingwritten and illustrated disclosure focuses on disclosing exemplaryembodiments, it should be clearly understood that the same is by way ofillustration and example only and that the invention is not limitedthereto. The spirit and scope of the present invention are limited onlyby the terms of the appended claims. The following represents briefdescriptions of the drawings, wherein:

FIGS. 1A and 1B are block diagrams illustrating a configuration of animage forming apparatus according to an exemplary embodiment;

FIG. 2 is a block diagram illustrating the relation between the imageforming apparatus shown in FIG. 1B and a host device;

FIG. 3 is a block diagram illustrating a configuration of an end pointaccording to an exemplary embodiment;

FIG. 4 illustrates a USB packet analysis table according to an exemplaryembodiment; and

FIG. 5 is a flow chart illustrating a method for operating an imageforming apparatus in a low power mode according to an exemplaryembodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments, examples ofwhich are illustrated in the accompanying drawings, wherein likereference numerals refer to the like elements throughout. Theembodiments are described below in order to explain the presentinvention by referring to the figures.

FIG. 1A is a schematic block diagram illustrating a configuration of animage forming apparatus according to an exemplary embodiment.

Referring to FIG. 1A, the image forming apparatus 100 may include aUniversal Serial Bus (USB) interface unit 110 and a control unit 120.The image forming apparatus 100 may be printers, copiers, scanners,facsimile machines, or multifunction peripherals (MFPs) having combinedfunctions in a single device.

The USB interface unit 110 performs USB communication with at least oneexternal device. The at least one external device may be host devicessuch as personal computers (PCs).

The USB interface unit 110 may include a control interface unit 111 toperform USB control communication with the at least one external device,and a data interface unit 112 to perform USB data communication with theat least one external device.

More specifically, the USB interface unit 110 may be implemented as anend point which is a logical port. Detailed description is given belowwith reference to the following drawings.

The control unit 120 controls the overall operation of the image formingapparatus 100, and in particular, controls a low power mode and a normalmode of the image forming apparatus 100.

In the low power mode, the control unit 120 performs an event accordingto a signal input through the control interface unit 111, and in thenormal mode, the control unit 120 performs an event according to asignal input through the control interface unit 111 and the datainterface unit 112.

In the low power mode, if the control unit 120 receives a signal throughthe data interface unit 112, the control unit 120 enters the normalmode.

FIG. 1B is a block diagram illustrating a detailed configuration of theimage forming apparatus shown in FIG. 1A.

Referring to FIG. 1B, the image forming apparatus 100 may include a USBinterface unit 110, a control unit 120, a first memory unit 130, asecond memory unit 140, and a power supply unit 150. Among thecomponents of the image forming apparatus 100 of FIG. 1B, detaileddescription of components overlapping the image forming apparatus 100 ofFIG. 1A is not repeated.

The control unit 120 converts the normal mode into the low power mode ifa preset condition is satisfied, for example, if there is no command fora preset period of time. This is merely an example, and there may bediverse conditions for mode conversion.

In addition, the control unit 120 converts the low power mode into thenormal mode if a preset condition is satisfied. For example, when theimage forming apparatus 100 is a printer, if a panel key is input, aprinting service is requested, of a fax rings, the control unit 120converts the low power mode into the normal mode.

If the control unit 120 converts the normal mode into the low powermode, the control unit 120 copies a program to control the low powermode from the first memory unit 130 into an executable area of thesecond memory unit 140. The first memory unit 130 is main memory whichmay be implemented as, for example, dynamic random access memory (DRAM).The first memory unit 130 may store a program capable of supporting USBcommunication in the normal mode, applications, etc, including a USBdriver.

The second memory unit 140 may store a program capable of supporting thelow power mode, applications, and may be implemented as static randomaccess memory (SRAM).

The program to control the low power mode includes the USB driver. TheUSB driver includes only a routine which is in charge of processingcontrol end point and a routine which is needed to be woken to return tothe normal mode. The program to control the low power mode requireslower capacity compared with the USB program which is stored in thefirst memory unit 130.

If copying the program to control the low power mode is complete, thecontrol unit 120 cuts off the power supply to most of system modules andthe image forming apparatus 100 enters the low power mode.

In the low power mode, the control unit 120 checks whether or notinterrupt is caused by the control interface unit 111 or the datainterface unit 112.

If interrupt is caused by the control interface unit 111, the controlunit 120 processes a corresponding service.

If interrupt is not caused by the control interface unit 111 but causedby the data interface unit 112, the control unit 120 reads printingdata, stores the printer data in the second memory unit 140, returns tothe normal mode, and processes a corresponding service. This is merelyan exemplary embodiment. According to whether the USB is in First InFirst Out (FIFO) mode or in direct memory access (DMA) mode, the controlunit 120 may return to the normal mode and store printing data in thefirst memory unit 130.

More specifically, if interrupt is caused by the data interface unit112, that is, if a specific operation command is input by the datainterface unit 112, the control unit 120 stores data from the secondmemory unit 140 into the first memory unit 130 which is accessible bythe USB driver in the normal mode. In this case, all hardware becomesactive and if the USB driver begins its operation, the control unit 120processes the interrupt and subsequently following events.

That is, in the low power mode, the image forming apparatus 100according to the exemplary embodiment processes only a service input bythe control interface unit 111. This is because the second memory unit140 has limited storage capacity.

The power supply unit 150 supplies power to the first memory unit 130and the second memory unit 140 according to operation of the controlunit 120.

More specifically, the power supply unit 150 supports the low power modeby cutting off power to the first memory unit 130 and maintaining powersupply to the second memory unit 140.

The control unit 120 may be implemented as only a main controller whichsupports both the normal mode and the low power mode, or implementedseparately as a main controller, which supports the normal mode, and asub-controller, which supports the low power mode.

If the control unit 120 is implemented as only a main controller, thatis, if main firmware related to control of the normal mode and microfirmware related to control of the low power mode are implemented on asingle chip, the low power mode may be implemented by lowering frequencyof the main controller as described above or configuring a gated clockin designing the main controller and thus cutting off clock input forblocks which do not operate in the low power mode. In this case, themicro firmware may be built in an inner memory (SRAM) of the maincontroller. The SRAM maintains data without refresh, and is thus fasterthan the DRAM in reaction rate. As a result, fast conversion is enabledfrom the low power mode to the normal mode.

To the contrary, if the control unit 120 is implemented separately as amain controller and a sub-controller, that is, if main firmware relatedto control of the normal mode and micro firmware related to control ofthe low power mode are implemented on respective chips, the low powermode may be implemented by supplying power only to the sub-controller.

In the exemplary embodiment, the control unit 120 is implementedseparately as a main controller and a sub-controller for convenience ofdescription.

FIG. 2 is a block diagram illustrating the relation between the imageforming apparatus shown in FIG. 1B and a host device. Among thecomponents shown in FIG. 2, detailed description of componentsoverlapping components described in FIG. 1B is not repeated.

The host device 200 may be implemented as a personal computer (PC) or auser terminal device such as personal digital assistants (PDAs) andportable media players (PMPs).

The host device 200 may include an application 210 and a host controller220.

The application 210 may be software supporting a USB function in anoperating system (OS).

The host controller 220 indicates a USB bus interface of the host device200, and includes all software and hardware which enable a USB device(that is, the image forming apparatus 100) to be connected to the hostdevice 200.

The host device 200 may further include a printer driver (unnumbered)which converts printing data written using an application program into aprinter language which can be interpreted by the image forming apparatus100. The printer driver may be included in the host controller 220. Inaddition, the host device 200 may further include general componentsconstituting host devices such as an input unit (not shown) and adisplay unit (not shown).

Hereinafter, general concept of an end point and a pipe is brieflydescribed for better understanding of the embodiments.

An end point is a logical port and is an end of flow of communication,which has a unique identification (ID). An end point includesinformation regarding data transmission direction (an input end pointand an output end point). An end point may include an access frequencyof a bus, requirements in delay of access of a bus, requirements forbandwidth, the number of end points, requirements for error handling,the maximum size of packet which the end point can accept, the type oftransmission, the transmission direction, etc.

A pipe is the link between an end point in a device and software in ahost. A pipe is divided into a stream pipe and a message pipe accordingto features. A stream pipe and a message pipe are different andexclusive. A stream pipe has no defined USB format and supports one-waycommunication. A message pipe has a defined USB format and supportstwo-way communication.

Detailed description of an end point and a pipe is omitted here sinceUSB specifications provide description thereof in detail.

The image forming apparatus 100 communicates with the host device 200through a USB, and has a control end point 111 (the control interfaceunit which is described above) and a plurality of end points 112 and 113(the data interface unit which is described above) in the USB interfaceunit 110. The end points except for the control end point 111 areslightly different according to a transmission method, but may be simplyconsidered as logical ports for data transmission and are thus referredto hereinafter as data end points.

The control end point 111 is a logical port to determine whether or notthe host device 200 is connected to the image forming apparatus 100through a series of procedures called enumeration, and, if connected, toobtain information regarding the image forming apparatus 100 or set theimage forming apparatus 100 to be communicable with the host device 200.That is, the control end point 111 is used while enumeration isperformed or a device on a bus operates (when the device is recognized).Accordingly, the control end point 111 is a basic end point to be incharge of connection/removal/recognition of a device, so any deviceshould have one. In addition, the control end point 111 should be alwayscontrollable.

The control end point 111 uses a message pipe unlike the data endpoints, and thus enables two-way transmission.

The data end points 112 and 113 are used for data transmission, and maybe at least one of bulk type IN/OUT end points, isochronous type IN/OUTend points, and interrupt type IN/OUT end points.

A bulk type IN/OUT end point exactly transmits comparatively a hugeamount of data, with a total disregard for time, and retransmits data ifa transmission error may occur in the bus. For example, a bulk typeIN/OUT end point may be used for data transmission of a storage devicesuch as a hard disk. In addition, a bulk type IN/OUT end point uses astream pipe, and thus supports one-way transmission.

An isochronous type IN/OUT end point is used mainly for devices whichvalues real-time communication such as audios above everything else,uses a stream pipe, and thus supports one-way transmission.

An interrupt type IN/OUT end point is used mainly for devices which needperiodical signal transmission and reception, uses a stream pipe, andthus supports one-way transmission.

In general, since the image forming apparatus 100 requires largequantity of transmission, a bulk type IN/OUT end point may be used.

The data end points 112 and 113 may select the number and the directionaccording to feature of interface. A manufacturer may selectivelydetermine the number and function of the data end points 112 and 113according to specifications of the device.

For example, a configuration of end points of a multifunction peripheralis shown in FIG. 3.

In FIG. 3, if it is assumed that an interface I 112′ is for a printerand an interface II 113′ is for a scanner, an OUT end point 112′-2 ofthe interface I 112′ is an end point for receiving printing data from ahost device 200′, and an IN end point 113′-1 of the interface II 113′ isan end point for transmitting scanned data from the host device 200′. InFIG. 3, the host device 200′ includes first and second host controllers220′-1 and 220′-2. The first and second host controllers 220′-1 and220′-2 may include device drivers I and II, respectively (unnumbered).

A main controller 121 controls the normal mode.

That is, the main controller 121 controls a basic function of an imageforming apparatus 100′ such as copying, scanning, faxing, etc in thenormal mode.

In addition, the main controller 121 converts the normal mode into thelow power mode if a preset condition is satisfied, for example, if thereis no command for a preset period of time. This is merely an example.When a specific user command is input, the main controller 121 mayconvert the normal mode into the low power mode.

That is, if the image forming apparatus 100 does not perform any job orif there is no operating command such as copying, scanning, and faxingwhich can be input using diverse user interfaces such as a panel on theimage forming apparatus 100, a USB or a network for a preset period oftime, the main controller 121 converts the normal mode into the lowpower mode.

If the main controller 121 converts the normal mode into the low powermode, the main control unit 121 copies a program to control the lowpower mode from the first memory unit 130 into an executable area of thesecond memory unit 140. The first memory unit 130 is main memory whichmay store a program required for the overall operation of the imageforming apparatus 100, applications, etc. The first memory unit 130 maybe implemented as DRAM and the second memory unit 140 may be implementedas SRAM.

The program to control the low power mode includes the USB driver. TheUSB driver includes only a routine which is in charge of processingcontrol end point and a routine which is needed to be woken to return tothe normal mode. The USB program which is stored in the second memoryunit 140 requires lower capacity compared with the USB program which isstored in the first memory unit 130, and can thus be implemented as lowcapacity memory.

If copying the program to control the low power mode is complete, thepower supply to most of system modules including the first memory unit130 is cut off and the image forming apparatus 100 enters the low powermode.

In the low power mode, the sub-controller 122 checks whether or notinterrupt is caused by the control end point 111 or the data end point112.

If interrupt is caused by the control end point 111, the sub-controller122 processes a corresponding event by executing the program andapplication stored in the second memory unit 140.

If interrupt is not caused by the control end point 111 but caused bythe data end point 112, the control unit 120 reads printing data, storesthe printer data in the second memory unit 140, returns to the normalmode, and processes a corresponding service. This is merely an exemplaryembodiment. According to whether the USB is in First In First Out (FIFO)mode or in direct memory access (DMA) mode, the image forming apparatus100 may return to the normal mode and store printing data in the firstmemory unit 130.

More specifically, if interrupt is caused by the data end point 112,that is, if a specific operation command is input by the data end point112, the image forming apparatus 100 stores data from the second memoryunit 140 into the first memory unit 130 which is accessible by the USBdriver in the normal mode. In this case, all hardware becomes active andif the USB driver begins its operation, the image forming apparatus 100processes the interrupt and subsequently following events.

The components illustrated in FIGS. 1 to 3 and the disposition thereofare merely an exemplary embodiment, so some elements may be deleted andmore elements can be added according to circumstances. Their dispositionalso may change.

FIG. 4 illustrates a USB packet analysis table according to an exemplaryembodiment.

Referring to FIG. 4, the printer driver 220 of the host device 200transmits a manufacturer limitation or class limitation request to theimage forming apparatus 100 through the control end point (end point 0:ENDP 0) on occasion. The subsequently following bulk transmission is aprinting command through end point 1 (see reference letter “A”). Thismeans that in the low power mode, requests may be continuously generatedthrough the control end point. Such a manufacture limitation request mayvary according to the manufacturer.

If the image forming apparatus 100 receives requests as shown in FIG. 4,the sub-controller processes requests for the control end point fromTransfer 48 to Transfer 64. Subsequently, if the image forming apparatus100 receives a printing command such as Transfer 65 through end point 1,the low power mode changes to the normal mode and the main controllerprocesses a corresponding event.

FIG. 5 is a flow chart illustrating a method for operating an imageforming apparatus in a low power mode according to an exemplaryembodiment of the present invention.

Referring to FIG. 5, in operation S510, in the low power mode, it ischecked whether or not interrupt is caused by the USB interface unit.

In operation S520, if interrupt is caused by the USB interface unit, itis determined whether or not the interrupt signal is caused by thecontrol interface unit.

In operation S530, if the interrupt signal is caused by the controlinterface unit, the image forming apparatus processes a correspondingevent.

In operation S540, if the interrupt signal is not caused by the controlinterface unit but caused by the data interface unit, the image formingapparatus returns to the normal mode.

Subsequently, in the normal mode, the image forming apparatus performsall events requested through both the control interface unit and thedata interface unit.

The control interface unit performs USB control communication and may bea control end point.

The data interface unit performs USB data communication and may be adata end point, that is, all end points other than a control end point.

The control end point is a logical port to determine whether or not thehost device is connected to the image forming apparatus through a seriesof procedures called enumeration and, if connected, to obtaininformation regarding the image forming apparatus or set the imageforming apparatus to be communicable with the host device. That is, thecontrol end point is used while enumeration is performed or a device ona bus operates (when the device is recognized). The control end pointuses a message pipe unlike the data end point, and thus enables two-waytransmission.

The data end point is used for data transmission, and may be at leastone of bulk type IN/OUT end points, isochronous type IN/OUT end points,and interrupt type IN/OUT end points. The data end point uses a streampipe, and thus supports one-way transmission.

The normal mode is controlled by the main controller and the low powermode is controlled by the sub-controller.

Applications and programs which are needed to operate in the normal modemay be stored in external memory such as DRAM.

Applications and programs which are needed to operate in the low powermode may be stored in internal memory such as DRAM.

If the image forming apparatus operates in the low power mode, the powersupply is cut off to the external memory used in the normal mode and thepower supply is maintained to the internal memory used in the low powermode.

As described above, according to the exemplary embodiment of the presentinvention, although the power supply is cut off to the main memory inwhich the USB driver operates, USB communication is enabled normally.Using small-capacity SRAM in the SOC, cost for an additional SRAM may besaved and the low power mode may be effectively implemented.

In the exemplary embodiment of the present invention, an image formingapparatus is described, but this is merely an example. The technicalidea of the present invention may also be applied to any kinds ofelectronic devices capable of USB communication.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. An image forming apparatus, comprising: a control interface unit toperform Universal Serial Bus (USB) control communication; a datainterface unit to perform USB data communication; and a control unit toperform an event in a low power mode according to a signal input throughthe control interface unit, and to perform an event in a normal modeaccording to a signal input through the control interface unit and thedata interface unit.
 2. The image forming apparatus according to claim1, wherein in the low power mode, if a signal is input through the datainterface unit, the control unit converts the low power mode into thenormal mode.
 3. The image forming apparatus according to claim 1,further comprising: a first memory unit to be used in the normal mode; asecond memory unit to be used in the low power mode; and a power supplyunit to supply power to the first memory unit and the second memoryunit, wherein if the image forming apparatus operates in the low powermode, the control unit controls the power supply unit to cut off thepower supply to the first memory unit.
 4. The image forming apparatusaccording to claim 3, wherein the control unit comprises: a maincontroller to control operation of the image forming apparatus in thenormal mode; and a sub-controller to control operation of the imageforming apparatus in the low power mode.
 5. The image forming apparatusaccording to claim 4, wherein in the low power mode, the sub-controllerchecks whether or not interrupt is caused by the control interface unitor the data interface unit.
 6. The image forming apparatus according toclaim 5, wherein if interrupt is caused by the control interface unit,the sub-controller processes an event related to the interrupt, and ifinterrupt is caused by the data interface unit, the sub-controllerconverts the low power mode into the normal mode.
 7. The image formingapparatus according to claim 1, wherein the control interface unit is acontrol end point, and the data interface unit is a bulk type IN/OUT endpoint.
 8. A low power driving method of an image forming apparatus whichcomprises a control interface unit to perform Universal Serial Bus (USB)control communication, and a data interface unit to perform USB datacommunication, the method comprising: checking whether or not a signalis input though the control interface unit or the data interface unit ina low power mode; and if a signal is input through the control interfaceunit, performing an event according to the input signal, and if a signalis input through the data interface unit, converting the low power modeinto a normal mode.
 9. The method according to claim 8, furthercomprising: if the image forming apparatus operates in the low powermode, cutting off the power supply to a first memory unit which is usedin the normal mode, and maintaining the power supply to a second memoryunit which is used in the low power mode.
 10. The method according toclaim 8, further comprising: if the image forming apparatus operates inthe low power mode, cutting off the power supply to a main controllerwhich controls operation of the image forming apparatus in the normalmode, and maintaining the power supply to a sub-controller whichcontrols operation of the image forming apparatus in the low power mode.11. The method according to claim 8, wherein the control interface unitis a control end point, and the data interface unit is a bulk typeIN/OUT end point.